Spin drift: Why do people say it doesn't matter?

[Roddy]

A lot of the time I see spin drift come up people will say it's not worth worrying about. Well at 1000 meters my ballistic app says I will have about 10" of spin drift. Compared to wind that is pretty trivial but it's still 10".

Why do people say it's not important? It's not hard to factor it in. On my range cards I just note which distances to add 0.1 or 0.2 mils hold for drift.

I recently shot my .308 at 970 metersand tried to hit a milk jug. I didn't have the most stable position (bipod was on the roof my truck and I was on my knees on the toolbox so I couldn't get my weight behind it) but I managed to hit it after five or six shots.

I was shooting through a cut line I had hung streamers up in. They weren't moving at all, there was no wind. I held for spin drift when I hit it. I think spin drift mattered.

On a side note the jug was still there after I hit it. The only thing that I could see was the green colored water I had filled it with was half gone. Turns out the exit wound was only about 5" wide. The .308 loses a LOT of energy at 970 meters!

 

[CanuckR]

Realistically in today's world with everyone using pretty good ballistics solvers there is no reason not to factor it in.
However I can also understand the idea that it sort of "gets lost in the noise." In a situation where there actually is wind, was your miss actually spin drift? Or a bad wind call? It becomes harder to say for sure and becomes easier for people to forget about.

 

[rugbydave]

I could definitely see how it could get lost in the noise when it's windy out but I use the values that Ballistic AE gives me. Starts around 600 yards (0.1mil) and by 1050 it's 0.3 mil. I don't see why not to use it. I was watching a video on SH about the new Hornady 3DOF solver and apparently according to that research spin drift has less influence than previously thought. For what it's worth I shoot out to 870 yards weekly with a flag at my position and one at the target. I dial 0.2 mils of left windage for spin drift and when both flags are limp, I hit dead centre...

 

[Roddy]

I totally get the point of view that it is eas to dimiss it as wind. But unlike wind it is a constant and easy to account for. People say it is trivial but 0.2 mils is 0.2 mils. I wouldn't want my zero to be out that much.

I also see the coriolis (spelling?) effect mentioned in precision shooting literature and it has something seven times less effect than spin drift. In Ryan Cleckner's book he goes into detail about both then goes on to say he rarely accounts for them.

It just seems to me that everyone and their dog should take spin drift into account long before the coriolis effect is ever mentioned.

 

[dero338]

that's it, .1mill @ 600 yards. if you shoot this range at 12-24 inch plate, it may not matter. if your target is a clay bird, well then it does.

 

[Mystic Precision]

For those that compete at LR, spin drift is something that is accounted for... in the scope zero.

It most certainly has an effect and a simple fix.

Then the real fun begins...

Jerry

 

[rugbydave]

that's it, .1mill @ 600 yards. if you shoot this range at 12-24 inch plate, it may not matter. if your target is a clay bird, well then it does.

Yeah, I figure shooting at a 12" wide plate (2/3 ipsc) at 870 yards that 0.2 mils of spin drift is 6 1/4" which would put 1/2 my rounds to the right of the target so why not account for it?

 

[Ryan.M.Anderson]

This is just my guess but I have a feeling that in the PRS world it is low on the list of things to be worried about.

After building a solid position, taking into acccount the wind, and dialing the correct distance all under a time limit there is not much time to worry about it.

I don't know about you guys but I can't really hold .2 mil when I am shooting off of barricade/barrel/tank trap/chain link fence.

Does anyone have the Applied Ballistics book? Maybe there is something in there about that.

 

[Roddy]

Does anyone have the Applied Ballistics book? Maybe there is something in there about that.

Brian Litz mentions it and that it is real. I don't remember exactly what his conclusion was but he believes in eliminating all variables.

I do know he said it was very difficult to measure due the amount of external variables, especially wind. How Litz measured it was he had two rifles made that were identical, same barrel and twist rate, except one had a left hand twist and one had a right hand twist. They were fired simultaneously and the distance between the two groups was divided in half to determine actual spin drift. Kind of neat.

I heard the M1903 Springfield had a slight curve to the rear volley/ladder sight to take spin drift into account. If they could do that over a century ago you would think scope manufacturers today could take it into account somehow.

I appreciate all the responses. This is something I have been curious about.

 

[BadAsMo]

Spin drift is surely real, but is not much of a priority to a competitive long range string shooter, because he can always walk them in.

If a guy had to make a perfect first round hit, spin drift would be much more of a key point of focus.

So if you're a PRS shooter who is taking one shot and moving onto a different target, it's to his advantage to understand spin drift.

An F-Class shooter with 2 convertible sighters before a 10 round string doesn't care so much, but with one caviat. The vertical shift caused by spin when the wind changes speed or direction is something that is best anticipated.

 

[Ryan.M.Anderson]

Brian Litz mentions it and that it is real. I don't remember exactly what his conclusion was but he believes in eliminating all variables.

I do know he said it was very difficult to measure due the amount of external variables, especially wind. How Litz measured it was he had two rifles made that were identical, same barrel and twist rate, except one had a left hand twist and one had a right hand twist. They were fired simultaneously and the distance between the two groups was divided in half to determine actual spin drift. Kind of neat.

Minor derail - is the book worth it? I was reading a discussion on SH yesterday and there was talks about how annealing/neck tension has a much smaller impact than anticipated and some other things about reloading. End derail.

 

[cdnshooter]

For those that compete at LR, spin drift is something that is accounted for... in the scope zero.

It most certainly has an effect and a simple fix.

Then the real fun begins...

Jerry

Interest peaked. Can you school me on this please?
Ben

 

[Roddy]

Minor derail - is the book worth it? I was reading a discussion on SH yesterday and there was talks about how annealing/neck tension has a much smaller impact than anticipated and some other things about reloading. End derail.

Short answer is yes.

I bought it on Kindle. A couple things I didn't really like such as no index so it is difficult to reference a particular topic. A lot of the book is about ballistic coefficients. While that is important it's almost a moot point because once you buy bullets you can't do anything to change BC. It is good to know though.

On the plus side reading the book was like reading ten times that much information on gun forums plus Litz has done the real world testing to back up what he says. The spin drift test is a great example. He does a really good job with this stuff. Wind, BC, velocity, air pressure, and lots more are very well covered and you can learn exactly how these things affect a bullet in flight.

Another really neat part is where uses accurate computer modeling to show the effects of different variables on long range shooting. For example is it better to have a half moa gun and make a poor wind call or a one moa gun and make a slightly better wind call. Helps you decide where you want to invest your training and money.

Overall lots of good info. It even for a long range shooting enthusiast it is a heavy read and am expensive book

 

[Mystic Precision]

Interest peaked. Can you school me on this please?
Ben

For most common set ups, the spin drift is pretty much 1/2 min to 3/4 min at 100yds when it arrives at 1000yds. Set you zero to the left a schnick and send it.

Adjust from there. In looking at a number of rifle set ups over the years, it is more common for a shooter to have a poor zero then correct... so before the bullet even leaves the barrel, the shooter has induced an error to the firing solution. Zero it properly at 100yds and many issues related to the rotation, inclination of the Earth can be taken care of long before it becomes a problem

100yds or m, cold bore shot then 3 more. Where did they land? If it didn't go into the dead center of your aiming point, worry about this before worrying about more nuanced problems.

Simple.

Jerry

 

[long range shooter]

Spin drift does matter at long distance (i.e. greater than 6oo m). When shooting at longer distances and wanting a first round hit you must consider spin drift, wind, air density, bullet BC and velocity, coriolis effect, and the eotvos effect just to name a few. The longer the shot, the more important these items become. Once the first shot is taken (and assuming your rifle has the same cold bore shot characteristics as the second shot) then it is a simple correction based on the actual impact point.

Cheers

 

[rugbydave]

This is just my guess but I have a feeling that in the PRS world it is low on the list of things to be worried about.

After building a solid position, taking into acccount the wind, and dialing the correct distance all under a time limit there is not much time to worry about it.

I don't know about you guys but I can't really hold .2 mil when I am shooting off of barricade/barrel/tank trap/chain link fence.

Does anyone have the Applied Ballistics book? Maybe there is something in there about that.

If the targets in a stage I'm shooting are past 600, I dial 0.1mil of left windage before the stage starts, 0.2 if the targets are past 800. I just concentrate on making a good wind call and breaking a good shot once the timer starts...

 

[gunlaker]

For most common set ups, the spin drift is pretty much 1/2 min to 3/4 min at 100yds when it arrives at 1000yds. Set you zero to the left a schnick and send it.

Adjust from there. In looking at a number of rifle set ups over the years, it is more common for a shooter to have a poor zero then correct... so before the bullet even leaves the barrel, the shooter has induced an error to the firing solution. Zero it properly at 100yds and many issues related to the rotation, inclination of the Earth can be taken care of long before it becomes a problem

100yds or m, cold bore shot then 3 more. Where did they land? If it didn't go into the dead center of your aiming point, worry about this before worrying about more nuanced problems.

Simple.

Jerry

Jerry, you guys are fortunate that it's not such a big factor. I shoot NRA mid and long range black power target rifle. At 600 it's about 1.5 minutes in my .40 cal rifle, and at a thousand it's around 4 minutes for my .45. If you don't compensate for it in our sport you won't even place, let alone win.

Chris.

 

[Mystic Precision]

Jerry, you guys are fortunate that it's not such a big factor. I shoot NRA mid and long range black power target rifle. At 600 it's about 1.5 minutes in my .40 cal rifle, and at a thousand it's around 4 minutes for my .45. If you don't compensate for it in our sport you won't even place, let alone win.

Chris.

I have had the pleasure of shooting beside BP at 1000yds F class matches... the fact that they hit consistently, blows me away. So much harder but they do it and do it well.

For most modern centerfire set ups, the adjustment for spin drift is pretty simple... just add 1/4 min left for each 300yds. Missing the target is not going to be spin drift caused.

Jerry

 

[ivo]

If the targets in a stage I'm shooting are past 600, I dial 0.1mil of left windage before the stage starts, 0.2 if the targets are past 800. I just concentrate on making a good wind call and breaking a good shot once the timer starts...

Not attacking anyone here but:

I don't think this will translate to a hit or miss either way on a 2 MOA target especially with external factors like wind, hold, shooting position....
In PRS, spin drift is completely irrelevant. Just my opinion of course.

 

[rugbydave]

Not attacking anyone here but:

I don't think this will translate to a hit or miss either way on a 2 MOA target especially with external factors like wind, hold, shooting position....
In PRS, spin drift is completely irrelevant. Just my opinion of course.

Yeah, I agree that it doesn't compare with wind, hold, shooting position etc but it's a calculated variable so I don't see why you wouldn't include it? I figure might as well eliminate the variables that you can.